Integrating with… GNS3!

On this page, I will discuss all the little pitfalls and issues with running this platform. I personally worked with the startup team since I was the former Manager of Support Services and the Documentation Strategist.

I discovered in this brief chapter of my life, it wasn’t GNS3 specifically, but I do have a knack for integrating things that works so well together. What you get from that is the very best of my experiences and my methodology for building super cool ‘sandboxes’.

GNS3 is an excellent place to start when you fall under this situation:

  • Very little experience with routers…(specifically any Cisco IOS router). You can incorporate other vendors to be sure, but the IOS is one that is so cumbersome and varies between builds, that for a new user, it’s a bit labyrinthine. I promise, I will spell everything out. For one who desires to become a network engineer, I will tell you all my little mistakes and hopefully you will benefit from it!

Consider this post a stub of more interesting sections to be added on this one page.

  1. I created a virtual box machine and loaded Ubuntu LTS. Since I left GNS3, I needed to learn quite a bit more in the Linux Distro worlds. I prefer using the Unity version of Ubuntu. the repos now have suitable versions of GNS3 where you won’t need to access the actual site and register. We’ll get into the reasons why it makes sense to do Linux instead of Windows, but if you must because you are running some older version of Windows and you don’t have enough memory and CPU, then go to and there you will find all the work I wrote on Windows support. But on my personal preferences, (since this is MY BLOG), I am going to recommend everyone to use a Linux distro and just “sudo apt-get install gns3“.*
  2. Within GNS3, there are two devices. They are both switches with layer 3 capabilities, however, one is designated as the router. On that note, GNS3 as a platform is really the best out there to get familiar with all kinds of wonderful routers and switching virtual machines. But at some point, you will have to invest in the equipment for which you are planning to support. That’s key. It’s not so much I’m a “Cisco Super Fan or Champion”, or any other vendor. But I want you to be able to MIRROR exactly the environment you are in. THAT’s the goal. Not to rip off the good folks at Cisco, or to somehow use this knowledge to harm companies. But I do want to empower you. If you don’t have money…don’t worry I’ll help you get the most out of the Internet and most importantly OUT OF YOURSELF!

Just think of me as a good buddy in the tech space (if you don’t have one).

It’s my sincerest wish that everyone gets an opportunity to be a success. If you’re not afraid to work, then you’ve come to the right place!

* if you actually type in sudo apt-get install gns3, you will most likely get gns3 version 0.8.7. That’s fine for basic pen testing on your local machine, however, if you need the updated version that supports IOU images, you need to search for the one that has IOU support. THAT version is preferred. Unfortunately, you would need to be running Ubuntu 64bit.

  1. sudo add-apt-repository ppa:gns3/ppa
  2. sudo apt-get update
  3. sudo apt-get install gns3-gui

Fundamentals with GRE

In this section, I break down how to look at a diagram in a book (like the CCNP Route from Cisco Press) and actually construct a REAL working model. To DO that, you need to have a CCNA level of understanding and a good understanding of how to get around GNS3.

On these two prerequisites, I will walk you through looking at a picture and “filling in the blanks” to get to the point of the topic at hand.

On page 54, Figure 2-4 in the book “CCNP Routing and Switching ROUTE 300-101 Official Cert Guide” it displays a topology example of what GRE is.

I went ahead and built the actual test lab in lieu of the illustration below:


Comments about the above pic:

1. I color coded which commands should be applied to which router. I chose GREEN  for the configuration in Router 1 and a weird orange thing for Router 4.

2. To further emphasize the point, I added visual GRE tunnels with an arrow pointing to the direction the traffic will flow. If you see a “->” or a “<-“, I’m specifically denoting which direction the configuration or flow of data is going.

Here is the rub.

From the perspective of a new reader or even a CCNA, it is ASSUMED that you know how to configure all routers in between Router 1 and Router 4. There is quite a bit to do BEFORE getting to use the GRE commands.

In the next installment, I will layout in a gif, how to get all the routers configured to have GRE work across the routers.

The first gif will be setting up the interfaces:

1. Connecting them together.

2. Going into global config mode and configuring the Loopback 0 interfaces on each router.

3. Still in the global config mode, configure the IP address of only the CONNECTED interface.

4. Then picking a routing protocol. In this example, since they are all Cisco 3725, it makes sense to use EIGRP.

5. Finally after verifying all interfaces can ping to their adjacent locally connected router, check the route tables and see if you can ping all the interfaces from router 1 to router 4.

6. When you have finally gotten ALL THAT worked out, you can now do the GRE configs for router 1 to router 4.